PURPOSE: To contrive improvement of wearing resistance of a socket and a ball so as to increase detaching strength of a ball joint during operation by eccentrically forming a chamfering part, provided in the ball, by an amount equal to the eccentric amount of an inlet relating to the center of the ball.

CONSTITUTION: An inlet 12a of a socket 12 is eccentrically formed by a predetermined amount from the center O1 of the socket 12 by a degree such that a peripheral edge of the inlet 12a is not inscribed to a contour of the socket 12 as plane-viewed from an inlet side of the inlet 12a. On the other hand, a cylindrical chamfering part 14 is formed in each ball 13 in a manner wherein its fitting into the inlet 12a of the socket 12 is made possible when a connecting rod 10 is tilted at a predetermined angle β to the outer of a normal swivel region α. The chamfering part 14 is eccentrically formed by a distance equal to the eccentric amount of the inlet 12a in an opposite direction to a tilt direction of the connecting rod 10 relating to the center O1 of the ball 13.